Directionality of ultrafast electron transfer in a hydrogen evolving Ru-Pd based photocatalyst

Qing Pan, F. Mecozzi, Jeroen P. Korterik, Divya Sharma, Jennifer Lynn Herek, J.G. Vos, W.R. Browne, Jannetje Maria Huijser

Research output: Contribution to journalArticleAcademicpeer-review

19 Citations (Scopus)

Abstract

Directionality of electron transfer and long-lived charge separation are of key importance for efficient photocatalytic water splitting. Knowledge of the processes that follow photoexcitation is essential for the optimization of supramolecular assembly designs in order to improve the efficiency of photocatalytic hydrogen generation. Photoinduced intramolecular electron transfer processes within the hydrogen-evolving photocatalyst [Ru(bpy)2(tpy)Pd(CH3CN)Cl]2+ (RuPd; bpy = bipyridine, tpy = 2,2′:5′,2″-terpyridine) have been studied by resonance Raman, femtosecond transient absorption, and time-resolved photoluminescence spectroscopies. Comparison of the photophysical properties of RuPd with those of the mononuclear precursor [(bpy)2Ru(tpy)]2+ (Ru) enables establishment of a photophysical model ranging from the femtosecond to the submicrosecond domain. Optical excitation of Ru and RuPd populates both bpy- and tpy-based 1MLCT (metal-to-ligand charge transfer) singlet states, from where intersystem crossing (ISC) into corresponding 3MLCT triplet states occurs. Electron density localized on the peripheral bpy ligands can subsequently flow to the tpy bridging ligand by interligand electron transfer, which process occurs with a time constant of 32.5 (±1.5) ps for RuPd. Not all electron density undergoes this process, most likely due to a competing loss channel on the bpy ligand caused by vibrational relaxation occurring at a time scale of 9.1 (±0.4) ps. The relaxed 3MLCTbpy and 3MLCTtpy states have excited state lifetimes of 400 (±1) ns and 88 (±1) ns, respectively. Electron transfer from the tpy ligand to Pd may take place on a ∼100 ns time scale, but it is also possible that the final relaxed excited state is delocalized over the tpy ligand and the Pd center. The insight that optical excitation populates both the peripheral bpy ligands and the bridging tpy ligand, and that part of the electron density subsequently flows from the former to the latter, is important for the realization of efficient photocatalytic hydrogen generation. The next step is to make the interligand electron transfer process faster, by functionalizing the peripheral ligands with electron-donating moieties, and adapting the nature of the bridging ligand and the catalytic metal center
Original languageEnglish
Pages (from-to)20799-20806
Number of pages8
JournalJournal of physical chemistry C
Volume118
Issue number36
DOIs
Publication statusPublished - 2014

Fingerprint

Photocatalysts
Hydrogen
electron transfer
Ligands
ligands
Electrons
hydrogen
Photoexcitation
Carrier concentration
Excited states
excitation
Metals
water splitting
Photoluminescence spectroscopy
polarization (charge separation)
molecular relaxation
photoexcitation
metals
atomic energy levels
time constant

Keywords

  • IR-94990
  • METIS-306865

Cite this

@article{78b88cad678546a3980eddf3eddd0fcb,
title = "Directionality of ultrafast electron transfer in a hydrogen evolving Ru-Pd based photocatalyst",
abstract = "Directionality of electron transfer and long-lived charge separation are of key importance for efficient photocatalytic water splitting. Knowledge of the processes that follow photoexcitation is essential for the optimization of supramolecular assembly designs in order to improve the efficiency of photocatalytic hydrogen generation. Photoinduced intramolecular electron transfer processes within the hydrogen-evolving photocatalyst [Ru(bpy)2(tpy)Pd(CH3CN)Cl]2+ (RuPd; bpy = bipyridine, tpy = 2,2′:5′,2″-terpyridine) have been studied by resonance Raman, femtosecond transient absorption, and time-resolved photoluminescence spectroscopies. Comparison of the photophysical properties of RuPd with those of the mononuclear precursor [(bpy)2Ru(tpy)]2+ (Ru) enables establishment of a photophysical model ranging from the femtosecond to the submicrosecond domain. Optical excitation of Ru and RuPd populates both bpy- and tpy-based 1MLCT (metal-to-ligand charge transfer) singlet states, from where intersystem crossing (ISC) into corresponding 3MLCT triplet states occurs. Electron density localized on the peripheral bpy ligands can subsequently flow to the tpy bridging ligand by interligand electron transfer, which process occurs with a time constant of 32.5 (±1.5) ps for RuPd. Not all electron density undergoes this process, most likely due to a competing loss channel on the bpy ligand caused by vibrational relaxation occurring at a time scale of 9.1 (±0.4) ps. The relaxed 3MLCTbpy and 3MLCTtpy states have excited state lifetimes of 400 (±1) ns and 88 (±1) ns, respectively. Electron transfer from the tpy ligand to Pd may take place on a ∼100 ns time scale, but it is also possible that the final relaxed excited state is delocalized over the tpy ligand and the Pd center. The insight that optical excitation populates both the peripheral bpy ligands and the bridging tpy ligand, and that part of the electron density subsequently flows from the former to the latter, is important for the realization of efficient photocatalytic hydrogen generation. The next step is to make the interligand electron transfer process faster, by functionalizing the peripheral ligands with electron-donating moieties, and adapting the nature of the bridging ligand and the catalytic metal center",
keywords = "IR-94990, METIS-306865",
author = "Qing Pan and F. Mecozzi and Korterik, {Jeroen P.} and Divya Sharma and Herek, {Jennifer Lynn} and J.G. Vos and W.R. Browne and Huijser, {Jannetje Maria}",
year = "2014",
doi = "10.1021/jp506269h",
language = "English",
volume = "118",
pages = "20799--20806",
journal = "Journal of physical chemistry C",
issn = "1932-7447",
publisher = "American Chemical Society",
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Directionality of ultrafast electron transfer in a hydrogen evolving Ru-Pd based photocatalyst. / Pan, Qing; Mecozzi, F.; Korterik, Jeroen P.; Sharma, Divya; Herek, Jennifer Lynn; Vos, J.G.; Browne, W.R.; Huijser, Jannetje Maria.

In: Journal of physical chemistry C, Vol. 118, No. 36, 2014, p. 20799-20806.

Research output: Contribution to journalArticleAcademicpeer-review

TY - JOUR

T1 - Directionality of ultrafast electron transfer in a hydrogen evolving Ru-Pd based photocatalyst

AU - Pan, Qing

AU - Mecozzi, F.

AU - Korterik, Jeroen P.

AU - Sharma, Divya

AU - Herek, Jennifer Lynn

AU - Vos, J.G.

AU - Browne, W.R.

AU - Huijser, Jannetje Maria

PY - 2014

Y1 - 2014

N2 - Directionality of electron transfer and long-lived charge separation are of key importance for efficient photocatalytic water splitting. Knowledge of the processes that follow photoexcitation is essential for the optimization of supramolecular assembly designs in order to improve the efficiency of photocatalytic hydrogen generation. Photoinduced intramolecular electron transfer processes within the hydrogen-evolving photocatalyst [Ru(bpy)2(tpy)Pd(CH3CN)Cl]2+ (RuPd; bpy = bipyridine, tpy = 2,2′:5′,2″-terpyridine) have been studied by resonance Raman, femtosecond transient absorption, and time-resolved photoluminescence spectroscopies. Comparison of the photophysical properties of RuPd with those of the mononuclear precursor [(bpy)2Ru(tpy)]2+ (Ru) enables establishment of a photophysical model ranging from the femtosecond to the submicrosecond domain. Optical excitation of Ru and RuPd populates both bpy- and tpy-based 1MLCT (metal-to-ligand charge transfer) singlet states, from where intersystem crossing (ISC) into corresponding 3MLCT triplet states occurs. Electron density localized on the peripheral bpy ligands can subsequently flow to the tpy bridging ligand by interligand electron transfer, which process occurs with a time constant of 32.5 (±1.5) ps for RuPd. Not all electron density undergoes this process, most likely due to a competing loss channel on the bpy ligand caused by vibrational relaxation occurring at a time scale of 9.1 (±0.4) ps. The relaxed 3MLCTbpy and 3MLCTtpy states have excited state lifetimes of 400 (±1) ns and 88 (±1) ns, respectively. Electron transfer from the tpy ligand to Pd may take place on a ∼100 ns time scale, but it is also possible that the final relaxed excited state is delocalized over the tpy ligand and the Pd center. The insight that optical excitation populates both the peripheral bpy ligands and the bridging tpy ligand, and that part of the electron density subsequently flows from the former to the latter, is important for the realization of efficient photocatalytic hydrogen generation. The next step is to make the interligand electron transfer process faster, by functionalizing the peripheral ligands with electron-donating moieties, and adapting the nature of the bridging ligand and the catalytic metal center

AB - Directionality of electron transfer and long-lived charge separation are of key importance for efficient photocatalytic water splitting. Knowledge of the processes that follow photoexcitation is essential for the optimization of supramolecular assembly designs in order to improve the efficiency of photocatalytic hydrogen generation. Photoinduced intramolecular electron transfer processes within the hydrogen-evolving photocatalyst [Ru(bpy)2(tpy)Pd(CH3CN)Cl]2+ (RuPd; bpy = bipyridine, tpy = 2,2′:5′,2″-terpyridine) have been studied by resonance Raman, femtosecond transient absorption, and time-resolved photoluminescence spectroscopies. Comparison of the photophysical properties of RuPd with those of the mononuclear precursor [(bpy)2Ru(tpy)]2+ (Ru) enables establishment of a photophysical model ranging from the femtosecond to the submicrosecond domain. Optical excitation of Ru and RuPd populates both bpy- and tpy-based 1MLCT (metal-to-ligand charge transfer) singlet states, from where intersystem crossing (ISC) into corresponding 3MLCT triplet states occurs. Electron density localized on the peripheral bpy ligands can subsequently flow to the tpy bridging ligand by interligand electron transfer, which process occurs with a time constant of 32.5 (±1.5) ps for RuPd. Not all electron density undergoes this process, most likely due to a competing loss channel on the bpy ligand caused by vibrational relaxation occurring at a time scale of 9.1 (±0.4) ps. The relaxed 3MLCTbpy and 3MLCTtpy states have excited state lifetimes of 400 (±1) ns and 88 (±1) ns, respectively. Electron transfer from the tpy ligand to Pd may take place on a ∼100 ns time scale, but it is also possible that the final relaxed excited state is delocalized over the tpy ligand and the Pd center. The insight that optical excitation populates both the peripheral bpy ligands and the bridging tpy ligand, and that part of the electron density subsequently flows from the former to the latter, is important for the realization of efficient photocatalytic hydrogen generation. The next step is to make the interligand electron transfer process faster, by functionalizing the peripheral ligands with electron-donating moieties, and adapting the nature of the bridging ligand and the catalytic metal center

KW - IR-94990

KW - METIS-306865

U2 - 10.1021/jp506269h

DO - 10.1021/jp506269h

M3 - Article

VL - 118

SP - 20799

EP - 20806

JO - Journal of physical chemistry C

JF - Journal of physical chemistry C

SN - 1932-7447

IS - 36

ER -